Am I going crazy or what?

This sounds like the beginning to a really bad horror movie. Please don't be one of the idiots in those movies who continue to ignore an obvious issue until something really bad happens. If I had a nanny and any one of these things had gone on (especially the not listening to my instructions part) I would have fired them long ago. Not only that, but shouldn't you be concerned about the safety of your child? You said you suspected the nanny of putting something in your child's food, and then you saw her on camera with some sort of powder? You're right, you are insane... for not firing her on the spot. And I'm sorry but what could possibly be your reasoning for not being able to find a new nanny? Do you live in a town with a population of four? Come on, take some responsibility and initiative.